In recent years, microcomputers and IC memories are widely used in electronic devices and in precision machines or instruments. However, they are vulnerable even to a momentary suspension of electric current, resulting in faulty operations or data erasure, for instance. For this reason, these devices and so forth generally have, as a backup power source, a small-sized capacitor in which an electric double layer is utilized. In such electric double layer capacitors, there has been used activated carbon which is electrochemically inert and has a large specific surface area. However, the conventional grades of activated carbon used for such purposes have a capacitance (electrostatic capacity) of at most about 60 F/g or, when expressed on a per-unit-volume basis, about 40 F/cm.sup.3 and are not fully satisfactory in this respect. Japanese Kokai Tokkyo Koho (published unexamined patent application) No. 63-78514 describes the use of an activated carbon species derived from petroleum coke and having a specific surface area of 2,000 to 3,500 m.sup.2 /g in manufacturing polarizable electrodes of electric double layer capacitors. However, this activated carbon is not fully satisfactory as yet from the viewpoint of capacitance, in particular capacitance per unit volume.